PROJECT SUMMARY/ABSTRACT Mammals are colonized with a vast and diverse consortium of microorganisms, collectively called the microbiota, that influence a wide array of biological processes. Recent studies demonstrate that in addition to their roles in nutrition, immunity and metabolism, the intestinal microbiota plays a fundamental role in the development and activity of the nervous system, influencing several complex host behaviors. The proposed research plan aims to uncover molecular and cellular mechanisms underlying the interaction between specific gut microbes and the brain, and to elucidate the impact of these relationships on host physiology. This research plan will investigate microbiome-gut-brain interactions that mediate the antiseizure effects of the ketogenic diet (KD). The KD is an effective treatment for refractory epilepsy and an increasing number of other brain disorders. However, use of the KD remains low due to difficulties with implementation, compliance and adverse side effects, and exactly how the diet succeeds in treating neural dysfunction in cases when drugs fail remains unknown. Understanding the molecular bases for KD-mediated protection against seizures will reveal new insights into signaling mechanisms from gut microbes to the nervous system and novel pathways for treating neurological disease. Notably, a previous publication from our laboratory reported that the KD results in striking changes in the gut microbiota, and these changes are required for the anti-seizure effects of the diet in two seizure models. We now propose to i) determine how the clinical KD influences the human gut microbiota in children with refractory epilepsy, ii) evaluate whether the KD-associated human gut microbiota regulates seizure susceptibility in mouse models for epilepsy, iii) uncover molecular and cellular mechanisms for microbial influences on neuronal activity. In doing so, we will consider the ability of microbes to modulate metabolomic profiles, sensory neuronal activity, ketone body levels and/or immune homeostasis as potential pathways for any microbiota-dependent host phenotypes. This work will push the frontiers of microbiota-gut-brain research toward uncovering new molecular pathways for treating neurological disease. The proposed research tests the transformative hypothesis that alterations in the human gut microbiome contribute to the anti-seizure effects of the ketogenic diet and could inspire novel strategies for enhancing the protective effects of the KD while overcoming major obstacles of strict dietary therapy. It is methodologically integrative in its study of neurobiology, drawing from advancements in functional genomics, metabolomics, gnotobiotics, imaging, molecular biology and neuroscience.